Electrostatic device



April 1945' K. w. OPPERMANN 2,373,140

ELECTROSTATIC DEVICE Filed Oct. 30, 1940 2 Sheets-Sheet l fix w W2 K JPVZ 10' man /kg m ATTORNEY K. w. OPPERMANN ELECTROSTATIC DEVICE 2 Sheets-Sheet 2 Filed Oct. 30, 1940 Kw-I mM ATTORNEY .trostatic devices.

' Patented Apr. 10, 1945 2,373,140 ELECTROSTATIC DEVICE Kurt W. Oppermann, River-head, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application October 30, 1940, Serial No. 363,473

17 Claims.

This invention relates to a new and useful electrostatic device employing a crystal which has a different dielectric constant in a plane at right angles to the crystallographic axis than in a plane which is parallel to the crystallographic axis a a dielectric medium.

An object of this invention is to improve electrostatic devices which are particularly adapted for usein an ultra-high frequency or short wave radio system.

Another object of thi invention is to provide a variable-electrostatic device of the solid dielectric type using a crystal, selectively cut at a predetermined angle with respect to its crystallographic axis, as the dielectric medium.

Still another object of this invention is to provide animproved electrostatic device which has a composite crystal dielectric and is interposed between two metallic electrodes. A feature of this novel'electrostatic device is the arrangement of a crystal having diiferent dielectric constants in different planes with respect to its major axis interposed between two electrodes whereby the permittance of the device is either of a desired predetermined value or varied by movement of either the crystal or one of the electrodes.

I have found that certain crystals, such as apatite, calcite, dolomite, Iceland spar and titanium dioxide (@102), of which rutile is the most abundant of them, possess two greatly diffe'ring values of permittivity (inductive capacity). The last mentioned crystals when measured at right angles with respect to the major crystallographic axis have a permittivity value equal substantially to 89 and when measured parallel to the major crystallographic axis the permittivity equals substantially 173. By my invention, I propose to use the property of such crystals as have different dielectric constants along different planes of their axis for fixed and variable elec- I am fully aware of the fact that electrostatic devices having a solid dielecreferring to the accompanying drawings, in which:

Fig. 1 shows how the dielectric crystal is cut from the mother crystal;

Fig. 2 i a plan view of the crystal shown in Fig. 1;

Fig. 3 is a section showing the crystal arranged with respect to two electrodes;

Fig. 4 is a section showing the minimum capacmade up of a composite crystal; and

Fig. 9 is a perspective view of .a composite crystal dielectric which is interposed between two electrodes.

Referring now in detail to Fig. 1, the crystal is shown as being that of a uni-axial titanium dioxide crystal, the major crystallographic axis of which is indicated by l. A cylindrical member tric are old in the art of variable condensers wherein such devicesemploy a solid dielectric of glass, mica or sulphur, but such materials have the same dielectric constant throughout and therefore should not be confused with the principles taught by this invention.

The device of this invention comprises briefly a pair of electrodes and a crystal such as for example one of titanium dioxide, the crystal being cut at a predetermined angle with respect to its mai or crystallographic axis and arranged to either be fixed or movable with respect to the :electrodes. This invention will best be understood by 3 is shown as being cut at a ninety degree angle line 2 with respect to the major crystallographic axis l.- After the cylinder is cut as optically predetermined to give a desired value, it is placed between two metal segments 4 and 5 and if provided with a shaft 6 it will be noted by referring to Fig. 4 that when in the minimum capacity setting the arrows I will indicate the direction of the crystallographic axis.

In Fig. 5, it will be noted that the arrows l for the maximum capacity setting are at ninety degree with respect to that shown by Fig. 4. Such a device will give a simple variable condenser or electrostatic device, which capacity between the two metal segments 4 and 5 will vary upon rotation of the cylinder from a maximum to a minimum of ninety degrees, this variation'of capacity resulting from the change of permittivity from the maximum to minimum, depending upon the rotation of the crystal and hence the position of its crystallographic axis in the electrostatic field between the condenser electrode plates. Although the showing in Figs. 1 and 2 indicates that a crystal is cut so that the axis of rotation of the cylindrical crystal is ninety degrees to the major crystallographic axis, solid cylinders may be' cut at other angles with respect to the major crystallographic axis in order to obtain diflerent ratios between the permittivity values of 89 to 173.

When a device having a smaller rate of capacity change is desired, crystals other than those of rutile may be employed. For example:

Apatite has a diel. const. of 9.50 at the .1. axis,

7.40 at the H axis.

I Beryl has a diel. const. of 7.85 at the .L axis,

7.44 at the H axis. Calcite has a diel. const. of 8.49 at the .l. axis,

7.56 at the [I axis. Dolomite has a diel const. of 1.80 at the .l. axis,

6.80 at the H axis.

Iceland spar has a diel. const. of 8.5 at the .l. axis,

struction, the center metallic portion N forms one electrode of the condenser and metal members i2, i3 and i l form the other electrode of the condenser. As mentioned above, the arrows 1 indicate the direction of the crystallographic axis and it will be noted that by rotation of members ill and l i, the capacity of the condenser will be varied and the principle of operation as mentioned above in connection with Figs. 4 and 5 generally applied to this embodiment.

The condenser embodiment shown in Figs. 6 and 7 is particularly adapted to a construction wherein a higher capacity value is desired.

Fig. 8 indicates a rotor mounted upon shaft 6 which is of composite construction made up of synthetic material, which is produced from powdered rutile or other similar crystals having the same general characteristics and a suitable insulation binding material 2| having properties similar to that of the single crystal of rutile wherein the particles 2'2 are oriented by any suitable means with the crystallographic axis arranged in one direction, while the binder is in a semi-plastic state and later allowed to be hardened. Such suitable means are disclosed in the Meissner Pat-' ents #l,969,379 and #l,99'7,263.

A still further embodiment of this invention is shown in Fig. 9 wherein a composite sheet 38 of powdered rutile is built up in the form of a thin flexible sheet dielectric for use as a fixed condenser and is interposed between two metallic electrodes 3| and 32. If desired, the metallic electrodes 3! and 32 may be flexible. Such a device is particularly desirable for short wave-circuits for reasons of its very high permittivity and excellent power factor. For example, I have found that when such a device is placed in a circuit having a frequency of one megacycle, the

phase angle equals substantially .06 whereas that of high grade quartz equals .03. Other advantages of such a synthetic sheet dielectric is that it will permit considerable reduction in the physical dimensions of electrostatic devices havin equal capacities due to its very highfpermittivity. Furthermore, by varying the proportions of crystal, rutile powder, through binder material of various permittivity, must be produced at will.

Although only a few embodiments of this invention have been shown, it is to be distinctly understood that it should not be limited thereto.' What is claimed is:

1. An electrostatic device comprising two electrodes, a crystal element having a difierent dielectric constant, along different planes passing through and making diiierent angles with its major crystallographic axis, said crystal being interposed between said electrodes, and means to move the crystal element and its major crystallographic axis with respect to said electrodes in order to present difierent values of permittivity of said crystal element between said electrodes and thereby change the capacity of said electrostatic device comprising said two electrodes and said crystal element.

2. An electrostatic device comprising two fixed electrodes, a crystal element having different values of dielectric constant along difierent planes through its crystallographic axis, said crystal intermsed between, said fixed electrodes, and means to move the crystallographic axis of said crystal with respect to said fixed electrodes to change the permittance there'between to vary the "capacity of said device.

3. An electrostatic device comprising two electrodes, a cylindrical crystal element between said electrodes, said cylindrical crystal element having been out such that its axis of rotation is substantially perpendicular to the major crystallographic axis of the mother crystal from which it was cut whereby rotation of the crystal about its axis of rotation causes said electrostatic device to have different values of capacity,

4. An electrostatic device comprising two arouate electrodes, a solid cylihdrical crystal element having difierent values oi dielectric constant along different planes through its crystallographic axis, said crystal interposed between said electrodes, and means to move the c ystallographic axis of said crystal with respect to said electrodes 6. An electrostatic device comprising two arcu ate electrodes, a solid cylindrical member of crystal particles oriented with their crystallographic axis in one direction and secured by a binding member, said crystals having different value of dielectric constant along difierent planes through their'crystallographic axes, said solid cylindrical member interposed between said electrodes with its periphery facing the arcuate surface of each electrode, and means to move said solid cylindrical member with respect to said electrodes to' change the permittance therebetween to vary the capacity of said device.

7. An electrostatic devicecomprising two electrodes, a composite dielectric composed of an insulating binding material and a plurality of linely divided crystals of diiierent dielectric 'constants along difierent planes through their crystallographic axes all of said crystals oriented alonga plane of with respect to the major crystallographic axes, said electrodes being arranged in capacitive relationship with said composite dielectric.

8. An electrostatic device comprising two flexible electrodes, a composite dielectric composed of an insulating binding material and a plurality of finely divided crystals of diflerent dielectric constants along different planes through their crystallographic axes, said crystals all oriented along a plane of ninety degrees with respect to the major crystallographic axis, said composite material interposed between said electrodes.

9. An electrostatic device comprising two fixed electrodes, a crystal element of rutile interposed between said fixed electrodes, and means to move the crystallographic axis of said crystal with respect to said electrodes to change the capacity of the device.

10. An electrostatic device comprising two fixed electrodes, a crystal element of calcite interposed sheet composed of an insulating binding material and a plurality of finely divided crystals of different dielectric constants-along different planes through their crystallographic axes, said crystals all oriented along a plane of 90 with respect to the major crystallographic axes.

13. A short wave electrostatic condenser for use in a circuit in the order of one megacycle comprising two electrodes, a thin flexible composite dielectric sheet composed of an insulating binding material and a plurality of finely divided crystals of difierent dielectric constants along different planes through their crystallographic axes, said crystals all oriented along a plane of 90 with respect to the major crystallographic axes.

14. An electrostatic device comprising a fixed electrode, a movable electrode, a crystal element having difierent values o1. dielectric constant along different planes through its crystallographl0 axis, said crystal having its crystallographic axis arranged in a predetermined position and interposed between said electrodes, said crystal being secured to move with said movable electrode, and means to move said movable electrode and said crystal with respect to said fixed electrode to change the permittance therebetween to vary the capacity of said device.

15. An electrostatic device comprising a fixed electrode, a movable cylindrical electrode, a hollov' cylindricalcrystal element having difierent values of dielectric constant along different planes through its crystallographic axis, said crystal interposed between said electrodes, and means to movethe crystallographic axis of said crystal with respect to said fixed electrode to change the permittance therebetween to vary the capacity of said device.

16. An electrostatic device comprising a fixed electrode, a movable cylindrical electrode, a hollow cylindrical crystal element having different values of dielectric constant along different planes through its crystallographic axis, said crystal interposed between said electrodes, and means to move said crystal including a shaft secured to said'cylindrical electrode to rotate said crystal with respect to said fixed electrode to change the permittance therebetween to vary the capacity of said device.

17.-A variable condenser comprising a pair of metallic electrodes and a crystal rotatably mounted between the electrodes, said crystal having different values of permittivity in different directions taken in a plane perpendicular to the axis of rotation of said crystal whereby the capacity value of said condenser may be varied by rotating the crystal about its axis between said metallic electrodes.

KURT W. OPPERMANN. 

